docs: add Claude Code commands documentation to README

Add comprehensive documentation for the custom Claude Code slash commands
that enable GitHub-integrated feature development workflow:

- /create-feature: Create feature specs with requirements and implementation plan
- /publish-to-github: Publish features to GitHub Issues and Projects
- /continue-feature: Implement tasks one at a time with automatic GitHub updates
- /checkpoint: Create detailed checkpoint commits

Documentation includes:
- Prerequisites (GitHub CLI setup, project scopes)
- Step-by-step typical workflow guide
- Example terminal session
- Offline mode instructions
- Command files location

Also bumps package version to 1.1.26 for this documentation update.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

create-agentic-app/package.json

@@ -1,6 +1,6 @@
 {
   "name": "create-agentic-app",
-  "version": "1.1.25",
+  "version": "1.1.26",
   "description": "Scaffold a new agentic AI application with Next.js, Better Auth, and AI SDK",
   "type": "module",
   "bin": {